The present invention relates to two component room temperature vulcanizable silicone rubber compositions and more particularly the present invention relates to two component room temperature vulcanizable silicone rubber compositions which are shelf-stable.
Two component room temperature vulcanizable silicone rubber compositions are well known (RTV shall hereinafter be utilized to refer to room temperature vulcanizable). Generally such compositions comprise as a basic ingredient a silanol terminated diorganopolysiloxane polymer and a filler which is usually formed into one package and in a second package there is mixed an alkyl silicate or partial hydrolysis product of an alkyl silicate as a cross-linking agent, a metal salt as a curing promoter and other ingredients such as additives, fillers and plasticizers. An example of a two-component RTV compositions with nitrogen-functional self-bonding additives can be found in Bessmer et al. U.S. Pat. No. 3,888,815 which is hereby incorporated by reference.
Usually such compositions are packaged such that per 100 parts of the first or base component there is added 10 parts of the second or catalyst component. Further, some of the filler is sometimes incorporated in the second or catalyst component so as to increase the viscosity of the component so that it can be properly metered and pumped to a uniform composition. Such composition is mixed with the base component to form a uniformly mixed two component RTV composition to be applied as a roof coating or as an insulating glass sealant in further applications.
Normally there is utilized per 100 parts of the base composition from 1 to 15 parts and preferably 10 parts of the catalyst composition that is a 10 to 1 mixing ratio.
A plasticizing fluid was also utilized in the second catalyst component as a diluent. However, it was found that there were problems associated with such composition and in particular with a catalyst component of such composition. Thus it was found that mixing and preparing a catalyst component in which there are present a plasticizing fluid, an alkyl silicate cross-linking agent, a tin catalyst and a nitrogen-functional self-bonding additive that the composition would have certain defects. One of the defects that it would have was that soon after it was prepared it would decrease in viscosity rapidly to the viscosity of water so it could not be pumped properly into the rest of the composition. There was also the problem of oil separation, in that the polysiloxane fluid would separate out from the rest of the composition and it would be necessary to mix the oil back into the rest of the composition before the composition could be utilized. Further, there was formed in the composition hard rock like nodules which made the composition unusable in that it might be unsightly and also in that the nodules might clog up the nozzles of the pump being utilized to pump such composition.
Further, in some cases it was found that the nodules would increase to a size such that the composition would be unusable altogether. It was found that this occurred in compositions as soon as one month after they had been prepared even when the preparation of the catalyst component was carried out under a nitrogen atmosphere and the composition was packaged in the substantial absence of moisture and air.
One way of solving this difficulty was to remove all contaminants from the mixing vessel of each batch of catalyst component prepared. By removing the ingredients of the prior batch, it is meant that the vessel was completely emptied and scraped down of all composition before it was utilized to prepare a new batch of catalyst component. This was necessary even though the kettle was utilized to produce a batch of the same composition in the prior use of the kettle. The emptying and scraping down of the kettle in which the batch of catalyst composition was prepared would usually take about 24 hours and increased the cost of preparing the catalyst component by a factor of two to three. However, it was found that even with these clean out procedures the above defects would still appear.
Accordingly it was highly desirable to find a process by which such catalyst components could be prepared such that they would have a shelf stability of six months or more without the formation of nodules, without oil separation or with a minimum of oil separation and without any decrease of viscosity. In the mixing procedure utilized to mix the catalyst component prior to that of the present invention, the filler was wetted into the plasticizing polymer. The mixture was then dried at temperatures above 100.degree. C. under vacuum for at least two hours so as to remove all moisture from the filler and the plasticizing fluid. The mixture was then cooled and a pre-blend of a cross-linking agent, self-bonding additive and metal salt was added slowly while mixing. Thereafter the mixture was mixed for 30 minutes, an additional 20 minutes under vacuum to remove all air and then packaged under a nitrogen atmosphere in the substantial absence of moisture. As stated previously, the utilization of this procedure and the complete shut down and scraping of the mixing kettle so as to remove all parts of the prior mixed composition did not result in an altogether satisifactory composition as far as shelf-stability was concerned.
Further the requirement of a 24 hour shut down for scraping down of the mixing kettle resulted in an undesirable increased cost of the catalyst component. Accordingly, it was found highly desirable to develop a process or a means for producing a shelf-stable inexpensive catalyst component for an RTV composition.
It is one object of the present invention to provide for a shelf-stable RTV catalyst component for two-component RTV composition.
It is an additional object of the present invention to provide a inexpensive and efficient process for producing a shelf-stable catalyst component for a two-component RTV composition.
It is an additional object of the present invention to provide a process for producing a catalyst component for a two-component RTV composition in which the catalyst component is shelf stable and does not produce nodules upon standing, does not separate oil and does not decrease measurably in viscosity. These and other objects of the present invention are accomplished by means of the disclosure set forth hereinbelow.